Current telecommunication systems can offer to their users data rates that seemed out of reach just a few years ago. Optical fiber systems are among those offering the highest bandwidth and capacity. For example, on a grid spacing of 100 GHz, dense wavelength division multiplexing (DWDM) systems may support up to 40 bidirectional channels on a single fiber installed between a network point of presence (POP) and a local multiplexer-demultiplexer, serving each of 40 distinct users, each user having bitrates up to one hundred (100) gigabits per second (GBPS).
Whereas each channel is formed of the combination of one or more lambdas, or wavelengths, within one band or multiple lambdas across multiple bands, for example an L-band channel and a C-band channel in each direction, on the same optical fiber with 100 GHz spacing, means that at any point in time, 80 lambdas may be used simultaneously on a single fiber. With smaller grid spacing, such as with 50 GHz or smaller, the number of channels increases accordingly to 160, or even more for smaller grid spacing such as 25 GHz or 12.5 GHz. The present disclosure applies irrespective of the number of channels or fiber optic bands (C, L but also O, E, S, U).
Telecommunication operators oftentimes define their network provisioning practices as service-level agreements (SLA) for their users, defining parameters such as guaranteed data rates and availability guarantees. For example, some users may be satisfied with “good” availability guarantees and may enter with their service provider into a contractual agreement that a given high data rate will be available 99% of the time and that at least a limited data rate will remain available 1% of the time. Some other users may have very strict availability requirements, specifying for example that a high data rate will be available 99.999% of the time; this availability level is known to those skilled in the art as a “five nines” level.
Modern telecommunication systems are very reliable, but are nevertheless not entirely fault-free. Providing very high availability requires some level of network redundancy. Various solutions have traditionally been used for providing high-availability in telecommunication systems. However, these solutions are generally costly and may be inefficient.
A commonly known network topology assigns two neighbor nodes to each of its nodes, thereby forming a ring of nodes. Data exchanged between two non-neighbor nodes needs to pass through other nodes located therebetween along the ring. In case of a link failure between two given neighbor nodes, data may still pass through all other nodes along the ring, bypassing the failed link. This so-called ring topology is very reliable. However, as data between any two nodes must pass through other nodes located therebetween along the ring, each node needs to be dimensioned for supporting traffic from the entire network. Additionally, because data between any two nodes may transit through one or several other nodes, depending on their location on the ring, it is difficult to guarantee a low communication delay using the ring topology.
Of course, another fairly simple solution to the need for high availability may be to simply double a number of communications paths and/or of an amount of equipment usually provided for serving users under normal conditions. If a first communication path or a first set of equipment breaks, another set of equipment across a first communication path or across an alternative communication path may takeover the entire load, without loss of capacity or quality of service until normal network conditions are re-established. Other solutions may offer a somewhat reduced quality of service, using an ample amount of redundant equipment.
As a well-known example, a single Wavelength Division Multiplex Passive Optical Network (WDM-PON) 40-channel system at a first point of presence (POP) usually comprises up to 40 terminals (at full capacity) for generating 40 different wavelengths for 40 distinct users connected to the POP via a single optical fiber. In case of failure of a first WDM-PON POP or of a first fiber, an alternative POP also comprising up to 40 terminals connected towards one or more of the first 40 users via an additional fiber, may take over. Obviously, the cost of such a solution may be prohibitive as there would be a need to provide for as many terminals as end-users enlisted for protection against network failures, on both the first POP as well as on one or more alternative POPs.
A single transceiver at an alternative POP may serve the 40 users, in a pure time division multiplex fashion, by allocating on average 2.5% of a shared channel to each user. This solution is cost effective and may satisfy many users. In a time division multiple access fashion, using dynamic bandwidth allocation (DBA), an average distribution of timeslots in the shared channel may be apportioned differently between users. At certain times, shared use of a single transceiver may impair some users requiring high bitrates, preventing them from obtaining the desired quality of service.
Therefore, there is a need for cost effective network bandwidth allocation and redundancy solutions that provide high data rates for some data users.